This invention relates to .beta.-lactam antibiotics. In particular, it relates to a process and intermediates for preparing azetidin-2-ones substituted on the ring nitrogen with an .alpha.-(dialkyl or diarylphosphono)carboxymethyl group which are useful as antibacterials and as intermediates to bicyclic antibiotics.
Since the discovery of the monocyclic .beta.-lactam antibiotics and the carbapenems and carbacephems, considerable effort has been undertaken to provide synthetic routes for preparing these antibacterials. Often, the elaboration of the 4-membered .beta.-lactam ring is the key to the preparative route. U.S. Pat. No. 4,595,532 describes a process for preparing N-[(diethoxycarbonyl)methyl]substituted azetidinones and related esters via cyclization of .beta.-hydroxy amides formed with diethyl aminomalonate and .beta.-hydroxy acids. The process of this invention provides N-[(.alpha.-phosphono)carboxymethyl]azetidinones via cyclization of .beta.-hydroxy amides formed with aminophosphonoacetates and .beta.-hydroxy acids.